1. Field of the Invention
The present invention relates to a revolving deck for an earthmoving machinery such as a minimal rear-swing radius hydraulic excavator.
2. Related Art
In the related art, there has been widely employed the so-called xe2x80x9cminimal rear-swing radius hydraulic excavatorxe2x80x9d in which the swinging locus of the rear end portion of a revolving unit having vertically swinging equipment at its front portion is confined, as seen in a top plan view, within the width of left and right crawlers of a travel unit. This minimal rear-swing radius hydraulic excavator 30 will be described with reference to FIGS. 12 and 13. FIG. 12 is a side view of the minimal rear-swing radius hydraulic excavator of the related art, and FIG. 13 is a perspective view showing a revolving deck 33 of FIG. 12.
Over a travel unit 31, as shown in FIG. 12, there is revolvably mounted a revolving unit 32. On the upper face of the revolving deck 33 or the base of the revolving unit 32, there are mounted a cab 34, a machine cab including an engine 35a and a hydraulic unit 35b, a counter weight 36 and so on. To the central front portion of the revolving deck 33, on the other hand, there are swingably attached equipment 40 including a boom 41, an arm 42 and a bucket 43. These components of the equipment 40 are driven by a boom cylinder 44, an arm cylinder 45 and a bucket cylinder 46, respectively.
As shown in FIG. 13, the revolving deck 33 is constructed by forming a frame body 33a of a single circular plate and by welding a center bracket 33b for mounting the boom 41 and the boom cylinder 44 to the central front portion on the frame body 33a, and a rear bracket 33c for mounting the engine 35a and the counterweight 36 to the central rear portion, respectively. On the other hand, the frame body 33a is equipped at its left portion with a bracket 33d for mounting the cab 34 and at its right portion with a bracket 33e for mounting the hydraulic unit 35b and so on. To suitable portions of the frame body 33a, there are additionally welded a variety of brackets and reinforcing members. To the outer periphery of the frame body 33a, moreover, there are attached left and right revolving guards 37 and 38 by means of bolts 39.
If the frame body 33a of the revolving deck 33 is made of the single plate, however, the plate thickness has to be increased to retain the rigidity thereby to invite a problem that the increased weight raises the cost. Since the left and right revolving guards 37 and 38 are attached by the bolts 39, on the other hand, there is the problem that they fail to contribute to the strength of the frame body 33a. 
In order to solve these problems, there have been proposed several techniques in the related art.
As a first related art of the revolving deck for the hydraulic excavator, there is a technique of the revolving frame of a hydraulic excavator, as disclosed in Unexamined Published Japanese Utility Model Application No. 87455/1994, for example. FIG. 14 is a perspective view showing the revolving frame of the Utility Model Application. In this Application, a frame body 51, a fender 52, a counter weight 53, an oil tank 54 and so on are integrally cast.
As a second related art, on the other hand, there is a technique of a revolving frame of an earthmoving machinery, as disclosed in Unexamined Published Japanese Patent Application No. 88617/1998, for example. According to this Japanese Patent Application, as shown in FIG. 15, of a left side frame 62 forming part of the structure of a revolving frame 61, a sectional shape of a rear frame portion 62B for supporting a machine room 71 and so on from the lower side is made larger in the vertical (or height) direction than a front frame portion 62A for supporting a cab 72 and so on from the lower side. Of individual overhanging beams 63, 64, 65, 66 and 67 overhanging leftward and rightward from the central portion of the revolving frame 61 to the front frame portion 62A and the rear frame portion 62B, on the other hand, the front side overhanging beam 64 having its leading end side jointed to the rear frame portion 62B is made to have a larger sectional shape.
However, the following problems are left unsolved in the related art described above.
The technique, as disclosed in Unexamined Published Japanese Utility Model Application No. 87455/1994, can have effects of a high rigidity and an improved assemblability for a small-sized machinery, because the frame body 51, the fender 52, the counter weight 53 and the oil tank 54 are integrally cast. For a medium- or large-sized machinery, however, the weight is drastically increased and also strength is required. As a result, difficulty is encountered in its manufacture, and the drive power required for the entire machinery is increased. Thus, problems arise in the fuel consumption, the performance of the machinery and the cost for its manufacture.
In the revolving frame disclosed in Unexamined Published Japanese Patent Application No. 188617/1998, on the other hand, the front portions of the front frame portion 62A and a right side frame 68, as seen in a top plan view, are located outside of the tail swing radius of the counter weight 73 so that they fail to conform with the so-called xe2x80x9cminimal rear-swing radius typexe2x80x9d. As a result, this failure may allow the revolving frame to contact with an obstacle at those overhanging portions.
In view of the aforementioned problems of the related art, the invention has an object to provide a revolving deck for an earthmoving machinery, which is shaped to have no contact with an obstacle within the tail swing radius of a counter weight and which has a structure of a high rigidity but not a large weight.
In order to achieve the object, according to a first aspect of the invention, there is provided a revolving deck for an earthmoving machinery, comprising: a main frame including a revolving unit mount portion and mounting a counter weight on its rear end portion; side decks arranged on the left and right sides of the main frame; and side frames disposed at the outer ends of the side decks, wherein the swinging locus to be drawn by the rear end portion of the counter weight is confined, as seen in a top plan view, substantially within the swing arc of the revolving deck. The revolving deck is formed, as seen in the top plan view, to be substantially within the width of a crawler, and the side decks are made of an integral skeleton structure including a plurality of overhanging beams jointing the main frame and the side frames.
According to the first aspect of the invention, the revolving deck is formed within the tail swing radius substantially equal to the counter weight so that it does not contact with an obstacle within this radius. Further, the revolving deck is given an integral skeleton structure in which the main frame and the side frames are jointed by a plurality of overhanging beams (or side decks), so that the weight can be made less than that of a single plate structure or a cast structure. On the other hand, even a medium- or large-sized hydraulic excavator can be easily manufactured with this simple structure so that its cost can be lowered. Because of the integral skeleton structure, moreover, many openings can be formed in the lower face of the revolving deck to improve the maintenance from the bottom of the deck.
According to a second aspect of the invention, the side frames of the first aspect are made to act as guards for protecting the overhanging beams and the main frame from an external force.
According to the second aspect, the side frames are made to act as the guards (or revolving frame guards) for protecting the overhanging beams and the main frame from external forces. As a result, these guards can provide reinforcing members for the frames to lighten the weight and reduce the number of parts so that the parts can be easily serviced, lowering the cost.